1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a facsimile, or a printer.
2. Description of the Related Art
In general, in image forming apparatuses using an electrophotographic process, a surface of an image carrier such as a photosensitive member is uniformly charged, and then an electrostatic latent image is formed on the image carrier by exposing the image carrier to light according to image data.
In such image forming apparatuses, when the image carrier is charged using mainly a corona charger. The corona charger charges the image carrier by applying high voltage to a metallic wire to cause corona discharge.
On the other hand, stains inevitably become attached to the metallic wire itself due to corona discharge, and it is thus necessary to clean the metallic wire on a regular basis. Further, the metallic wire may be required to be replaced. Moreover, a large amount of ozone is produced due to corona discharge.
An electrophotographic photosensitive member is affected by ozone product (discharging or charging product) generated by reaction of ozone produced from a charger and moisture in the air, and hence when repeatedly used, the surface of the electrophotographic photosensitive member gradually becomes sensitive to humidity and tends to absorb moisture.
As described above, when ozone product becomes attached to the surface of the photosensitive member which have become sensitive to humidity, the surface resistance of the photosensitive member decreases due to ozone product, and so-called image deletion occurs in which an electrostatic latent image is deleted.
To prevent such image deletion, there has been proposed the technique that a photosensitive member is shielded from a charger when an image forming apparatus switches from a standby state of being ready to form images into a sleep state which is a power saving mode (see Japanese Laid-Open Patent Publication (Kokai) No. 2007-72212). Here, when the image forming apparatus switches into the sleep state, the photosensitive member and the charger are shielded from each other so that ozone product can be prevented from becoming attached to the photosensitive member and deteriorating the durability of the photosensitive member and causing image deletion.
However, according to Japanese Laid-Open Patent Publication (Kokai) No. 2007-72212, if a user turns off main power supply to the image forming apparatus before the image forming apparatus switches from the standby state into the sleep state, the photosensitive member and the charger cannot be shielded from each other.
When the image forming apparatus is left in the state in which the photosensitive member and the charger are not shielded from each other, ozone product becomes attached to the photosensitive member. In this state, if main power supply is turned on, and a print job is executed, image deletion occurs during the execution of the print job because ozone product is attached to the photosensitive member.